CST Load Cell Wiring & Troubleshooting 3

Question 1

Which symptom most strongly suggests moisture ingress into a load cell or junction box?

Accepted Answer

Erratic, drifting zero with no applied load

Answer

Moisture causes leakage currents across the bridge circuits, producing an unstable, drifting zero reading.

Question 2

What is the purpose of a shielded cable in load cell wiring?

Accepted Answer

To reduce electromagnetic interference (EMI) on the signal lines

Answer

Shielding surrounds the signal conductors and is grounded at one end to divert induced EMI noise away from the load cell output.

Question 3

During troubleshooting, a technician finds that shorting the signal wires together causes the indicator to read exactly zero. What does this confirm?

Accepted Answer

The indicator and its wiring back to the junction point are functioning correctly

Answer

Shorting the signal inputs confirms the indicator circuit reads zero when given a true zero-differential input, isolating the fault to the load cell side.

Question 4

What value should the input resistance (signal+ to signal−) of a healthy 350 Ω load cell measure?

Accepted Answer

Approximately 350 Ω

Answer

For a 350 Ω load cell, the signal bridge output resistance (input resistance) is nominally 350 Ω when measured across the signal terminals with excitation disconnected.

Question 5

Which load cell specification directly describes the maximum combined error from non-linearity, hysteresis, and repeatability?

Accepted Answer

Combined error or accuracy class

Answer

Combined error (accuracy class) is the single specification that encompasses non-linearity, hysteresis, and repeatability as a percentage of rated output.

(CST) Certified Scale Technicians Practice Test

(CST) Certified Scale Technicians Practice Test

CST Load Cell Wiring & Troubleshooting 3